ZOONOTIC DISEASE HISTORY
Of the worlds’ new and emerging diseases, approximately
75% are zoonotic!!
These emerging infectious diseases make the role of the
veterinary health care professional extremely important!
Veterinary health care professionals help prevent disease in
animals and humans.
Besides producing diseases in humans, zoonotic diseases can affect the food
chain – for example Brucellosis.
The environment may also affect zoonotic diseases. For example, changing
ecosystems have resulted in an increase in tropical diseases.
With the domestication of animals, changing culture has played a role in the
development of zoonotic diseases.
Human disease itself has played a role in the increase of zoonotic disease!!!
With the increase of immunosuppressive conditions and drugs (chemotherapy
and HIV) physicians are concerned that their patients with pets may be more
susceptible to zoonotic disease.
There are more than 150 known zoonotic diseases, however fewer than ½ of them are
clinically significant.
(Think ‘The Black Plague”, tuberculosis, Lyme disease)
Term: Sentinel
A domestic animal host for a particular disease that is placed at various
locations to determine the potential for human exposure to a particular disease.
Chain of Infection
Pathogen
Susceptible Host
Reservoir
Portal of Entry
Portal of Exit
Mode of Transmission
Reservoir: an animate (living) or inanimate (non-living) object that serves as a
long-term habitat and focus of dissemination for an infectious agent.
Living reservoirs include humans, animals and arthropods (insects, arachnids,
crustaceans)
Vector: any live animal that transmits an infectious agent from one host to the
next (typically used to describe arthropods)
Biological Vectors: actively participate in a pathogen’s life cycle, serving
as a place where the pathogen multiplies or
completes its life cycle.
Infectious agents are spread via
injecting infected saliva into blood, defecating
around the wound, regurgitating blood into the
wound bite, aerosol formation or touch
Ex: mosquitoes, fleas, ticks
Mechanical Vectors: are not necessary for the life cycle of the pathogen
and are passive participants in the transmission
of disease.
Spread disease when their external body parts
become contaminated through contact with the
pathogen.
Transferred to human or animals indirectly by an
intermediate such as contaminated food or
directly by contact between the contaminated
body part and a mucous membrane or skin
surface
Ex: houseflies, cockroaches
Non living reservoirs :
air
soil
dust
food
milk
water
fomites (objects that are able to transfer disease organisms)
Transmission:
Direct transmission – the immediate transfer of an infectious
agent from a reservoir to a susceptible host
Ringworm
Indirect transmission: the transfer of an infectious agent carried from a
reservoir to a susceptible host.
West Nile Virus
Direct and Indirect transmission occurs by a variety of mechanisms:
* Contact: occurs through touch and may be either direct or indirect
Ex: a human touches the skin lesions of a ringworm positive cat
and then transfers the ringworm. (direct)
Ex: a person touches the skin of a ringworm-positive cat then
touches another cat transferring the fungal spores to the
second cat that then gets ringworm (indirect)
* Airborne droplets of respiratory secretions may contain pathogens
and have the ability to spread disease via aerosol.
Ex: sneeze or cough from the infected animal to an uninfected
animal (direct)
Ex: sneeze that contaminates a ventilation system that eventually
infects an animal/human (indirect)
* Placental transmission occurs from mother to offspring and is
form of direct transmission.
* Fomites (or vehicles) such as animal bedding that have become
contaminated by blood, saliva, urine, feces, vomit, exudates,
respiratory secretions, or milk may be a source of indirect
transmission
* Arthropods such as fleas, mosquitoes, lice, ticks, mites and flies
can indirectly transmit infectious agents.
Classification of Diseases
Acute: diseases that develop rapidly but last only a short time (common cold)
Chronic: diseases that develop slowly, usually with less severe clinical signs and are
continual or recurrent 9tuberculosis)
Latent: diseases in which a pathogen remains inactive for along periods fo time
before becoming active (herpes viral infections)
Infectious or communicable: a disease that is acquired from an infected host (flu)
Contagious: easily transmitted communicable diseases (chickenpox )
Noncommunicable: not spread from one host to another and diseased individuals
do not serve as a source of contamination for others (tooth decay)
Epidemiology
The study of the effects of diseases on the community. The frequency and distribution
of disease within a population is studied.
* microbe virulence
* ports of entry and exit
* course of disease
Epidemiologists are concerned with the who, what, where, when , why and how of
infectious diseases.
They monitor statistics to determine the frequency of a particular disease in a given
population.
Endemic: diseases that are always present within a population of a particular
geographic area.
Enzootic disease: conditions affecting animals of a specific geographic area –
constantly present in a specific animal community, but only
occurs in a small number of cases. (plague in prairie dogs)
Sporadic: when there are a few isolated cases of a disease, such as the plague in
humans, seen in widespread areas in an unpredictable manner
Epidemic: a disease with a sudden onset and widespread outbreak within a group
Epizootic: widespread disease in populations of animals – spread rapidly,
simultaneously affecting a large number of animals in a region
Pandemic: disease that is a widespread epidemic and generally involves the spread
across continents.
Panzootic: widespread epizootic disease.
Agencies
WHO: (World Health Organization) a specialized agency within the United
Nations.
Missions: 1. to promote cooperation for health care among nations
2. carry out disease control and eradication programs
3. improve the quality of human/animal life
When epidemics occur, WHO sends out teams of epidemiologists to investigate the
outbreak and to assist in bring the outbreak under control.
CDC: (Centers for Disease Control and Prevention: a United States federal
agency under the control of the U.S. Department of Health and Human
Services.
Function: to assist state and local health departments in all aspects of
epidemiology.
“to promote disease prevention and health promotion goals
that will foster a safe and healthful environment where
health is protected, nurtured, and promoted.”
One branch within the CDC is the National Center for Infectious
Disease (NCID) and its mission is “to prevent illness, disability,
and death caused by infectious disease in the United States and
around the world.”
NIH: National Institutes of Health – a division of the U.S. Department of
Health and Human Services – the primary federal agency for conducting
and supporting medical research.
Publishes guidelines for the care of animals in research facilities as well as the
prevention of disease transmission among animals and between animals and
humans.
NIH funds research on a variety of disease topics including zoonoses and ways
to prevent their spread.
NIH also educates the public and physicians about the role of zoonoses and
human health through providing information such as the role of pets and the
immunocompromised person.
At the federal level, the U.S. Department of Agriculture’s (USDA) Animal and Plant
Health Inspection Service (APHIS) requires licensed veterinary personnel to
report diseases that pose a significant threat to human health.
All information taken directly from Understanding Zoonotic Diseases by Janet Amundson Romich. Thomson Delmar
publishing